1. Field of the Invention
The present invention relates to an industrial robot having a foresight function into a work point yet to be worked with a workpiece shape sensor.
2. Prior Art
There are many types of industrial robots. Some of them have a sensor for tracing certain reference points or lines of a workpiece, e.g. a profile line prescribed on a workpiece surface. An arc welding robot of such a type detects the lines to be welded by monitoring electric current in the welding rod, and by controlling the position of the welding rod holder. Another type of robot stores a welded line data beforehand by an operator's teaching operation of guiding a tool tip along the welded line, and the tool tip then moves and machines on the workpiece in accordance with the stored data.
The former type of welding robot can trace the joint line at low working speed, but it cannot follow it at high speed, because it requires computational time to accurately recognize the position to be welded. When the position is accurately recognized, the welding rod is already out of position. The latter type of robot with the teaching data memory can trace the taught line at high speed in an actual job stage, but it requires the tracing action twice: one for teaching and the other for the actual job. The result is an overall work inefficiency.
As an advanced technology, laid open document of Japanese Unexamined Patent Application No. sho 59-223817 discloses a robot for controlling a tool to trace a joint line of work members by using a slitted light projector and a two-dimensional camera. As sensing and working are simultaneously executed by the robot, the operational time could be reduced. But still it has some drawbacks as follows.
(1) As the data processing of the sensed two dimensional image data requires a lot of time, usually more than several seconds for one frame of image, this robot is made to go directly on a straight line from the present working point to the next remote working point. Only a starting point and an ending point of the workpiece is previously taught to this robot but information on the points between them is not taught. The robot is controlled exclusively on information acquired from the sensor between those points. Therefore, when there is an unexpected steep irregular part between those points on the work surface, high tracing fidelity is impossible.
(2) When the sensor fails in the course of the work, the robot follows the erred data of the sensor, resulting in possible collision with the workpiece.